1. Field of the Disclosure
The disclosure herein relates generally to apparatus and method for producing visible light using laser emission.
2. Description of the Related Art
A variety of display systems, such as televisions and projectors, utilize light illumination systems to project images on display media. Image brightness is a useful metric in such display systems. The brightness can limit the size of a projected image and can be a factor in how well the image can be seen in high levels of ambient light. One approach to increasing brightness of a display has been to employ solid-state lasers. Conventional solid-state lasers typically emit light in infrared (IR) wavelengths. A frequency-multiplying optical element converts the IR laser emissions into visible light, such as red, green, or blue light, depending on the initial frequency or wavelength of the IR laser emissions. The resulting visible light may then be used to illuminate optical elements, such as a digital micromirror device (DMD) or a spatial light modulator (SLM) of the projection display system.
Often a filter, such as a Volume Bragg Grating (VBG), at the exit end of the frequency-multiplying element is used to pass a wavelength of narrowband (red, blue or green) light corresponding to the wavelength conversion properties of the frequency-multiplying element. Such a filter is aligned to reflect IR back to the relatively small aperture of the laser. A second filter at the interface between the laser and the frequency-multiplying element polarizes the light and passes the IR light. The second filter also is utilized to reflect the visible light back emission out of the frequency-multiplying element and the optical resonant cavity, which results in the use of additional optical and mechanical components that are relatively precisely aligned. The overall output efficiency of such systems can be relatively low. Accordingly, there is a need to provide an improved laser illumination system.